.\"	$OpenBSD: gpiodcf.4,v 1.5 2015/06/07 20:13:13 claudio Exp $
.\"
.\" Copyright (c) 2008 Marc Balmer <mbalmer@openbsd.org>
.\"
.\" Permission to use, copy, modify, and distribute this software for any
.\" purpose with or without fee is hereby granted, provided that the above
.\" copyright notice and this permission notice appear in all copies.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
.\" WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
.\" MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
.\" ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
.\" WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
.\" ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
.\" OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
.\"
.Dd $Mdocdate: June 7 2015 $
.Dt GPIODCF 4
.Os
.Sh NAME
.Nm gpiodcf
.Nd DCF77 timedelta sensor through GPIO pin
.Sh SYNOPSIS
.Cd "gpiodcf* at gpio? offset 0 mask 0x1"
.Cd "gpiodcf* at gpio?"
.Sh DESCRIPTION
The
.Nm
driver decodes the DCF77 time signal code using one GPIO pin.
The pin is used as a data signal.
The GPIO pin must be able to read an input.
.Pp
The pin number can be specified in the kernel configuration with the
.Ar offset
locator.
The
.Ar mask
locator should always be 0x1 in this case.
The
.Ar offset
and
.Ar mask
can also be specified when
.Nm
is attached at runtime using the
.Dv GPIOATTACH
.Xr ioctl 2
on the
.Xr gpio 4
device.
.Pp
.Nm
implements a timedelta sensor and the delta (in nanoseconds) between the
received time information and the local time can be accessed through the
.Xr sysctl 8
interface.
The clock type is indicated in the sensor description:
.Bl -tag -width "CRITICALXX" -offset indent
.It DCF77
German DCF77 time signal station
(77.5 kHz longwave transmitter located in Mainflingen near Frankfurt).
.El
.Pp
The quality of the timedelta is reported as the sensor status:
.Bl -tag -width "CRITICALXX" -offset indent
.It UNKNOWN
No valid time information has been received yet.
.It OK
The time information is valid and the timedelta is safe to use for
applications like
.Xr ntpd 8 .
.It WARN
The time information is still valid, but no new time information has been
decoded for at least 5 minutes due to a reception or parity error.
The timedelta should be used with care.
.It CRITICAL
No valid time information has been received for more than 15 minutes since
the sensor state degraded from OK to WARN.
This is an indication that hardware should be checked
to see if it is still functional.
The timedelta will eventually degrade to a lie
as all computer internal clocks have a drift.
.El
.Sh SEE ALSO
.Xr gpio 4 ,
.Xr intro 4 ,
.Xr ntpd 8 ,
.Xr sysctl 8
.Sh HISTORY
The
.Nm
driver first appeared in
.Ox 4.5 .
.Sh AUTHORS
.An -nosplit
The
.Nm
driver was written by
.An Marc Balmer Aq Mt mbalmer@openbsd.org .
